The invention relates to a spring-loaded parking-brake and service-brake system for trailers towed by motor vehicles.
An example of a spring-loaded parking-brake and service-brake system for trailers is shown in German patent Specification No. 2,720,632. In this system, a pneumatic signal corresponding to the actuation of the service brake in the motor vehicle is supplied to a control valve by a control-line coupling. The pressure medium controlled by the control valve and coming from the storage vessel then actuates the service brake of the trailer. Furthermore, the spring-loaded parking brake of the trailer is actuated by a trailer parking-brake valve which is controlled pneumatically by a manual parking-brake valve and a manual release valve connected to the parking-brake valve.
To apply the trailer parking brake, the parking-brake valve is brought into the parking position, with the result that the pressure medium from the storage vessel is applied to the lower relay piston of the trailer parking-brake valve. The lower relay piston is thereby pressed upwards and opens an outlet, through which the pressure medium flows out of the spring-loaded brake cylinders into the surrounding area.
If the braked trailer is to be maneuvered when uncoupled, the parking valve has to be brought into the driving position and the release valve pressed. As a result, pressure medium is supplied from the storage vessel to the spring-loaded parking brake by the trailer parking-brake valve and the spring-loaded parking brake is released. A further pneumatic connection between the supply line and the trailer parking-brake valve ensures, when the trailer breaks contact, that the spring-loaded parking brake is applied temporarily.
Because the service-brake and spring-loaded parking-brake systems are controlled in the above system by purely pneumatic means, the brakes can only react after a certain response time as a result of the time required for pressure to build up. Also, this system has a complicated and expensive design, since three different valves are provided in this brake system. These are the parking-brake valve, the release valve and the trailer parking-brake valve, each being of complicated design in itself and therefore expensive to produce. Furthermore, the trailer parking-brake valve is controlled by long lines with complicated routing, the disadvantages being that a very large amount of space is taken up, and also, line losses can occur.
A further disadvantage is evident in that when the trailer is maneuvered in the uncoupled state, the control lines are also bled in addition to the spring-loaded brake cylinders, with the result being that the air in the storage vessel is rapidly used up. Moreover, to make maneuvering possible, two valves first have to be actuated manually.
An adverse effect can also arise in the above-described system because the automatically actuated trailer parking brake is applied only temporarily when the trailer breaks contact or is uncoupled from the motor vehicle. In this state, the trailer parking brake can only be released as a result of pressure on the release valve, to put the trailer in an unbraked state. It is therefore only possible to park the uncoupled trailer safely if the driver sets the parking-brake valve to parking position.
After the trailer has been coupled again, the parking-brake valve has to be brought into the driving position again to release the spring-loaded trailer parking brake. In this state, however, the vehicle-trailer connection is retained only by the parking brake of the motor vehicle. Also, when the trailer is coupled, its spring-loaded parking brake cannot be actuated from the motor vehicle or at the same time as the parking brake of the motor vehicle. In particular, when the vehicle combination is parked or left standing, the driver must apply the parking brake in the motor vehicle, dismount and bring the lever on the parking-brake valve of the still unbraked trailer into the parking position. Only by doing this is the spring-loaded parking brake of the trailer applied. In general terms, therefore, safe parking of the trailer both when coupled and when uncoupled is possible only by actuating the parking-brake valve on the trailer and is therefore dependent on the conscientiousness of the driver.
An object of the present invention is to develop a spring-loaded parking-brake and service-brake for trailers, which provides for maximum possible safety despite a simple design, and which allows the uncoupled trailer to be maneuvered simply and safely.
These and other objects are attained according to the invention by providing a parking brake and service brake system for a trailer towed by a motor vehicle with a service brake and a parking brake in the trailer, a pressure medium supply device for supplying a pressure-medium, and a fluidic supply coupling means for fluidly coupling the motor vehicle and the trailer. A fluidic control-line coupling supplies a fluidic control signal from the vehicle to the trailer when the service brake of the vehicle is actuated. Also provided is a control valve for supplying a controlled amount of the pressure-medium to the trailer service brake in response to the fluidic control signal. This control valve is fluidly connected to the control-line coupling and the trailer service brake.
The system also provides a first electrical trailer coupling for transmitting electrical signals between the vehicle and the trailer, and a pilot valve for supplying a second fluidic control signal to the control valve in response to electrical signals from the first electrical coupling. This pilot valve is fluidly connected to the control valve and electrically connected to the first electrical coupling.
One advantage of the invention is that, in addition to the fluidic signal, an electrical signal is also used to control the service brake, thus making it possible for the service brake to respond rapidly and thereby increase safety.
An especially preferred embodiment of this system provides a second electrical trailer coupling for transmitting electrical signals between the vehicle and the trailer when either the parking brake of the motor vehicle is actuated or a randomly generated electrical signal is transmitted. A trailer parking brake valve supplies the pressure medium to the trailer parking brake in response to electrical signals from the second electrical coupling. The trailer parking brake valve is fluidly connected to the trailer parking brake and the storage vessel, and is electrically connected to the second electrical trailer coupling.
Substantial advantages are obtained by this preferred embodiment of the invention because of the electrical control of the trailer parking-brake valve. The use of an electrically controlled valve makes it possible to achieve a simple design of the spring-loaded trailer parking-brake system. Consequently, no valves differing from one another and that are complicated to produce are used, allowing for reduced production costs. Safety is increased because, when the trailer is coupled to the traction vehicle, its spring-loaded parking brake is actuated at the same time as the parking brake in the motor vehicle is actuated. The driver therefore does not have to additionally bring the spring-loaded parking brake of the trailer into the braking position, this normally being carried out by reversing a switch on the trailer.
Another advantage is that the spring-loaded parking brake automatically switches into the braking position when the trailer is uncoupled from the motor vehicle. Furthermore, the trailer remains fully maneuverable when uncoupled, since the spring-loaded trailer parking brake can be actuated by means of the randomly generated electrical signal which can be transmitted.
A further advantage is that, when the spring-loaded trailer parking brake is switched, only the air from the spring-loaded trailer parking-brake cylinders is used up. Moreover, after the trailer has been coupled again, the spring-loaded parking brake is automatically switched to "driving" or "braking" at the same time as the parking brake in the motor vehicle is actuated. In other words, the spring-loaded parking brake of the trailer remains in the braking position during the coupling of the trailer to the motor vehicle when the parking brake of the latter is set at "braking" and switches to "driving" when the parking brake of the motor vehicle is released.
A great advantage of preferred embodiments of this system is that the spring-loaded parking brake in the trailer is actuated completely automatically either at the same time as the parking brake in the motor vehicle is actuated or when the trailer is uncoupled, so that safe parking of the trailer is therefore carried out irrespective of the conscientiousness of the driver.
Additional features of a preferred embodiment of the present invention provide further advantages. For example, by providing that the pneumatic coupling parts and the electrical coupling parts form a single connection unit, the trailer can be fluidly and electrically connected to the motor vehicle all at once. This ensures that when the pneumatic connections are broken, the electrical connections are also broken at the same time, so that the trailer parking brake is actuated immediately.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.